Rotor for dynamo-electric machines



Sept. 25, 1928.

A. J. BROWN ROTOR FOR DYNAMO ELECTRIC MACHINES Filed July 18. 1921Patented Sept. 25, 1928 1 NITEDsT 'TEs -PM firms.

ARTHUR .1. BROWN, 0F MILWAUKEE, 'WISCONSINASSIGNOR T0 ALLIS-CHA'LMERSMANUFACTURING COMPANY, on MILWAUKEE, isconsin, A CORPORATIQN or DELA AE. 1 J

r I Boron FOR Dynamo-EL CTRIC MACHINES.

Application satin 18, 1921. Serial No. 485,652.- I

dynamo-machines and has particular relation to machines whereinthewindings are dispo'sedin slotted cores. H

In accordance with recognized practice in the design and constructionofcertain types of dynamo-electric machines, especially the rotor elementsthereof, the depth of the core slots in which the windings, aredisposed, and hence the amount. of copper in such windings, is limitedbythe fact that the thickness of the, teeth oft-he core adjacent thebottom or inner-portions of the slots,

that is, the cross-sectional area of thete'eth at the roots thereof,must-be of "a certain value in order to Withstand the mechanicalstresses set up in thecore during operation of the machine. This isespecially true in the case of the rotating field elements of highspeedmachines here the mechanical stresses, due to centrifugal force actingupon the teethand the windings in the slots, are liable to bejverygreat.

1 In certain types of machines, as for instance, high-speed,synchronous, alternating current machines, this matter of providingsufiicient slotispace 'for. the reception of the required 1 amount ofcopper "field, winding,

- without unduly increasing thediameter and length of the rotor core isof extreme impor- I tance', and the higher the speedof the machine, thegreater the importance. In the case of bipolarl generators, operating at3600 R. P. M., a type'of machine which is ordinarily used when thegenerator is ,driven by a steai1i:.-turbine, the rotor-must be i made ofas small a. diameter as possiblein order to reduce the peripheral speedand centrifugal force to a minimum. I Hence, it is. important from thestandpoints of cost and. efficient operation that the rotor v be of thesmallest sizethat canv carry the required amount of field copper toefficiently. producethe required"core flux, and also=that the core be ofsufhcient mechanical strength toi Withstand'the mechanical stresses setup therein,

,quiredininiinum thickness of the core teeth is preserved while Iproviding a, maximum viiiding spaceffor the reception of copper"WlIlCilIlg; This'construction includes the 5 provision of slots ofunequal depth and so disposed as to preserve sulhcient thickness at theroot portions of the teeth between the slots, so as to insure that allparts may safely withstand any stresses set .up therein duringoperation, and to preserve, the required crosssection ofthe magneticpath of the core at theradially innerends of the slots;

' It is an'object of this invention to provide any-improved design andconstruction of dynamoelectric machine wherein the. core slots are suchas to provide a. maximum winding space while preserving the desiredmechanical and magnetic characteristics :of the core. r A y It is afurther object of this invention to provide an improved design andconstruction of dynamo-electricmachine embodying a, rotatable coreelement having ,winding receiving slots of unequal size,while preserv-It is a further object of this invention to provide an improved designandconstruction oi dynamo-electric machine embodying a rotatable corewherein adjacent radially inseries located in radially disposed slots,

adjacentslots being of different depth and containing different amountsof copper winding, I

. These and other ob ects and advantagesare secured by this invention,the various novel, features of which will be-apparent i from} theaccompanying description and drawings, disclosing one embodiment of-thenvention, and are intended to be more par ticularly pointed, out in theclaims. 1 especially in the core teeth and the windings in. theaccompanyin drawings Fig. 1 is a front elevation, partly. in sec .tion,of a dynamdelectric machine whose rotary field'element embodies featuresof this invention.

Fig. 2 is a section taken along the plane 1 ofline II-II of Fig. l. a

ing the desired mechanicaland magnetic characteristics of the core.

In accordance with the disclosure of the drawings, a dynamo-electricmachine, of the type usually known as a turbo-generator, includes astator 12, constitutinga stationary armature and including a core andwindings disposed in slots therein, and a rotary field element 13. Therotary field element comprises a core 14;, which may be solid as hereshown, or made up of laminations arranged in groups with air spacestherebetween and held in operative position and mounted upon a shaft 15.The core is provided with an energizing winding 16, in the form of aplurality of turns arranged in a plurality of layers in the radial slots17, 18 ot the core. Teeth 19 are-formed by the slots 17, 18; and wedges20 coaet with the sides of the on er portions of the teeth to hold thewinding 16 in place within the slots. The slots 17', 18 are preferablyof the same width throughout, and the cross-sectional area of thewinding is preferably the same throughout all the turns of its fulllength. As is usual in the ordinary design, the winding 16 is laid inthe pair of slots nearest to or furthest from the axis of the polarportion 21 of the core untilthe required amount of winding is in placein such slots, and the winding is then disposed successively in thepairs of slots more or less remote from the axis of the pole 21.

In accordance with previous designs of the rotary field element of thistype of dynamoele'ctric machine, it has been customary to have the slotsall of the same depth with sufficient cross-sectional area at the rootsof the teeth to withstand the mechanical stresses due to centrifugalforce on portions of the teeth and the windings in the slots; and thiscross-sectional area at the roots of the teeth determined the depth ofthe slots and, hence. the amount of copper that might be included in arotor of a particular size and designed for a particular operatingspeed. In accordance with the present design, the slots 17 may be of adepth corresponding to the desired thickness or crosssectional area ofthe teeth at a point opposite the bottom of the slots 17, indicated at23; but the slots 18 may be extended radially inward to a dept-h that isdetermined especially in the case of a solid core, practically only bythe requirement that there be sufficient core material beyond theradially inner portion of the slot to provide the re quired magneticpath between the poles of the core.

With this design, it will be apparent that the requirement forsuflicient mechanical strength at the roots oi the teeth may be fullypreserved or complied with, and, in addition, provision is made forspace for disposing an additional amount of copper for energizingpurposes. In the particular embodiment of the invention illustrated, the

slots 17 contain 11 layers of winding, while the slots 18, with theirextra depth provide for 14: layers, thus providingfor approximatelyfourteen percent more energizing copper than might safely be disposed onthe same core it all of the slots were of the same de th as the slots17. y y '7 ihe effect or this added copper space in certain slots of anyparticular core is that with the additional winding available, the amiere turns required to give the desired fielil flux can be produced withless current density and, hence, with less I R'losses; and, in addition,with less current density in the winding, the amount of heat to be dissipated during operation of the machine is less, and-since the properdissipation of heat from the rotor core and winding is, at best, nosimple proposition, with lower current density andless heat producedbythe winding, the problem of properly dissipating this heat issimplified. Further, considerably greater energizing elfects may. besecured while maintaining a sufficiently low current density in thewinding.

In the embodiment ofthe inventionillustrated, the slots adjacent thepolar axis of the pole 21 are shallow slots 17; and under the moreordinary conditions of design, it will be found that the material of thecore can be better utilized, that is, from the standpoint of providingthe maximum amount of copper winding of suitable size, by having thosecore slots nearest to the polar axis, of the shallow variety. Byproviding the shallower slots adjacent the polar axes, as indicated inFigure 2, it will be apparent that the minimum cross-sectional area ofthe polar portion 21 can bemade a maximum, for the width of this polarportion is measured'between the adjacent portions of the inner ends ofthe slots at opposite sides of the axis of the pole; and it will beapparentthat' this thickness of the polar portion decreases as the depthof these slots increases. Y

A general eliect of utilizing this invention is to increase theefficiency and output of a machine having a core ofa certain size, or toobtain the same. output from a core of smaller size, in either caseproviding an obviously more desirable design and con struction than isofi ered by the prior art;

It should be understood that it is not desired that the inventionclaimed be limited to the exact details of construction shown anddescribed, for obvious modifications will readily occur to a personskilled in the art.

It is claimed and desired to secure by Letters Patent:

1. In a dynamo-electric machine, a rotor comprising. a core providedwith radially extending peripheral slots of substantially the same widthand different depth, and a winding disposed in said slots, adjacentslots Inn containing different total, cross-sectional areas of saidwinding, and winding elements 1110116 slot being connected in seriesrelaelectric machine, comprising a core provided substantially the samewidth and dilferent with radially extending peripheral slots of depth,and a winding disposed in said slots, the total cross-sectional. areaiofthe winding elements in a deeper slot being greater than that in ashallow slot, and a winding element in the deeper slotbeing connectedinseries relation with a winding element in the shallower slot. i

3. A rotary field element for a dynamoelectricmachine, comprising a coreprovided withperipheral, winding-receiving of substantially the samewidth and different depths, the slots immediately adjacent a olar axisof said core ,boin shallower than P 0 slots more remote from said axis.

4. In a dynamo-electric machine, a rotary field element comprisinga coreprovided with radially extending peripheral slots of substantially thesame width and difierent depth, the slots nearest the polar axes of isaid core being shallower than the slots immediately adjacent the firstslots, and a field energizing winding having portions disposed in eachof said slots. a

5. In a dynamo-electric machine, a rotary field element comprising acore provided with radially extending peripheralslots of substantiallythe same width and different depths, the slots immediately adjacent apolar axis of said core being shallower than slots moreieniote from saidaxis, and a' winding disposed in said slots, said winding being ofsubstantially the same cross-sectional area and shape throughout a fullturn thereof and having difi'erent numbers of layers in different slots.p

6. In a dynamo-electric machine, a bipolar rotary field elementcomprising a core provided with radially extending peripheral slots ofsubstantially the same width, the slots on each side of a polar axis ofsaid core beingot' different depths, and the slots immediately adjacentsaid polar axis being shallower than the'slots more remote from saidaxis, and a winding disposed in said ferent numbers of layers inadjacent slots.

In testimony whereof, the signature of the inventor is alfixed hereto.

ARTHUR J. BROWN.

